SPIN

Using the two-dimensional Jordan–Wigner Fermionization procedure, we calculate the energy spectrum of the in-phase flux antiferromagnetically spin-1/2 coupled Heisenberg model in a square lattice, the formalism used introduces the notion of isotropic parameters. The energy spectrum is analyzed for various regimes of the exchange interactions and the isotropic parameters. The thermodynamic parameters of the lattice, notably the ground state energy, the free energy, mean energy, entropy and specific heat are calculated. It is seen that the specific heat undergoes a phase transition at a temperature below the critical temperature due to spontaneous magnetization. Its entropy for homogeneous and completely isotropic regime is compared for two regimes of the exchange interaction and it is observed that the entropy decreases with an increase in the coupling strength. All the thermodynamic parameters calculated for this spin model are seen to be in conformity with the principles and laws of Statistical Thermodynamics.

The full potential linearized-augmented-plane-wave (FP-LAPW) method is generalized to a case of an all-electron fully-relativistic spin-polarized self-consistent band calculation based on the relativistic spin-density functional theory and the modified Becke–Johnson potential (TB-mBJ) plus an on-site coulomb U employed for greater generation of the band gap. The results show that these materials are semiconducting materials. The indirect energy gap obtained in this calculation is 1.63eV, 1.79eV and 1.96eV for EuS, EuSe and EuTe, respectively. It is clear from the plots that LSDA$+$U is a poor technique for the calculation of the band gaps of chalcogenides (EuX). The calculated results for EuX (S, Se and Te) by mBJ$+$U are in good agreement with the experimental values as compared to the other calculated results.

Understanding of different magnetic configurations for the FeAs₂ iron pnictide compound is carried out using first-principles studies based on spin density functional theory (DFT) within the generalized gradient approximation (GGA), including the spin–orbit coupling (SOC). The calculated stable phase is in the marcasite (Pnnm) with nonmagnetic spin-ordering. We find that the FeAs₂ compound in the nonmagnetic (NM) marcasite phase undergoes pressure-induced phase transition to the antiferromagnetic (AFM1) marcasite phase at 12GPa, then to the AFM CuAl₂ ($I$4/mcm) phase at 63GPa. The phase transition is also accompanied by semiconducting (marcasite phase) to metallic (CuAl₂ phase) transition. The calculated electronic density of states profile shows the hybridization of the Fe-3$d$ and As-4$p$ orbitals plays an important role in determining the electronic and magnetic characters of this compound. The associated phase transition results in increased Fe-3d orbitals around the Fermi energy level.

Spins-5/2 and 3/2 Ising octahedral chain with regularly alternating monomeric and square plaquette sites is investigated using Monte Carlo simulations. The ground state phase diagrams of octahedral chain have been found for different blocks $n$ and for a several reduced crystal fields. The magnetization and magnetic susceptibilities of the mixed spins Ising octahedral chain have been obtained. The variation of reduced the transition temperatures with 1/$n$ has been determined. The magnetic hysteresis cycles of the mixed spins Ising octahedral chain for several blocks, $n$, for several reduced crystal fields and reduced exchanges interactions for a weak a zero crystal field have been investigated.

We report on growth optimization and magnetodynamic properties of $\beta$-W/Co${}_{20}$Fe${}_{60}$B${}_{20}$ system. We show that a relatively low growth rate of $\sim 0.17$Å/s is essential for the stabilization of the $\beta$ phase of tungsten. The low growth rate allows for the residual oxygen present in the chamber to get incorporated into the growing film, which helps in the stabilization of $\beta$-phase tungsten as evidenced by X-ray diffraction and X-ray photoelectron spectroscopy. Using these optimized growth conditions, we achieved the $\beta$ phase in tungsten thin films up to a thickness of 60nm. The ferromagnetic resonance measurements of $\beta$-W/Co${}_{20}$Fe${}_{60}$B${}_{20}$ show a linear behavior of the Gilbert damping constant with the inverse of the thickness of the CoFeB layer, from which, we calculated spin mixing conductance to be $(1.62\pm 0.15)\times 10^{18}$m${}^{-2}$. Using the inverse spin Hall effect measurements, we obtained a large spin Hall angle of $-0.44\pm (0.04)$ in $\beta$-W, which is achieved without using oxygen plasma during growth of tungsten.

Using first-principles calculation within the generalized gradient approximation (GGA) and $\mathrm{\text{GGA}}+U$ (Hubbard Coulomb onsite correction), we investigated the structural, electronic and magnetic properties of CrS, CrSe and CrTe compounds in different phases. We found that the NaCl phase is the lowest energy structure in comparison to the other investigated phases within the $\mathrm{\text{GGA}}+U$ approach for CrS, CrSe and CrTe compounds. The CrX compounds investigated in the NaCl phase are all half-metallic ferromagnets with a net magnetic moment of 4.0${\mu }_{\mathrm{\text{B}}}$ within the $\mathrm{\text{GGA}}+U$ approximation. From the density of states profile and charge density distribution, the observed half-metallic ferromagnetism in the CrS, CrSe and CrTe compounds is due to the spin polarized 3$d$ orbitals of the Cr atoms. The observed stable half-metallic ferromagnetism in the NaCl phase of the CrS, CrSe and CrTe compounds should motivate further experimental studies on the possible application of these compounds as spintronic materials.

First-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate the structural, electronic and magnetic properties of KX ($\text{X}=\text{S}$, Se and Te) binary alkali–metal chalcogenides compounds. These compounds in different crystalline phases, NaCl (B1), CsCl (B2), ZB (B3), NiAs (B8${}_1)$, WZ (B4) and Pnma, were calculated within the generalized gradient approximation (GGA-PBE) and the modified Becke–Johnson approach (mBJ-GGA-PBE) for the exchange–correlation energy and potential. We found that the most stable phase for the KX binary compounds is the nonmagnetic Pnma phase. The calculated lattice parameters, bulk moduli, their first-pressure derivatives and internal parameters are in good agreement with the other theoretical data. The electronic band structure and density of states show that half-metallic and magnetic character arises, which can be attributed to the presence of spin-polarized $p$ orbitals in the group VI elements. KX ($\text{X}=\text{S}$, Se and Te) compounds, except for KSe and KTe in the CsCl and NiAs phases, show HM character in all phases, with an integer magnetic moment of 1${\mu }_{\mathrm{\text{B}}}$ per formula unit and HM gaps.

The magnetic properties of chromite ACr₂S₄ ($\text{A}=\text{Z}$n, Cd and Hg) spinels have been investigated. The first, second and the third nearest-neighbor exchange interactions are included into a Metropolis-based Monte Carlo calculation for the three-dimensional Ising model. Transition temperatures have been deduced from the variation of magnetizations and magnetic susceptibilities for three spinel systems. The magnetic hysteresis cycles have been deduced for three systems. Critical exponents associated with the magnetization, magnetic susceptibility and specific heat have been determined. Superparamagnetism behavior has been obtained below the transition temperature. The results of our simulations are in good agreement with other results.